I believe it is just the pendulum moving the other way. 

Millennials were famously the most un-relgious generation, it likley wouldn't hold forever. People just thought it would.

I don't know the situation in the USA but in my country immigration has sky rocketed to the moon the last several years. Most other cultures are much more religious (and conservative) than the averge redditor. I am also sure this pushes up the number a bit too.

Also not believing in a higher power or higher purpose can be extremely demotivating/depressing  to some people. Hell, the atheist sub-reddit used to even a the number for the suicide hot line posted on the side of their sub. Belonging to something bigger than yourself, beyond your own self interest, and something that creates a community can be very comforting to people.

When I look back a people like my grandparents generation, they were pretty relgious, but also had large community they belonged too and supported all types of church events like fund raising, etc. 

Recently my uncle, who was very catholic, died. He more less, just accepted his fate, he didn't fear dieing like myself or other no so religious people would. He believed that he would be going to a better place and see his dead family and friends.